Loud-speaking telephone receiver



M I l/ Filed May 16 W VAN B ROBERTS LOUD SPEAKING TELEPHONE RECEIVER April 15 1924.

WIT/V5885 Patented Apr. 15, 1924.

UNITED STATES PATENT OFFICE.

LOUD-SPEAKING TELEPHONE RECEIVER.

Application filed Kay 18, 1922. Serial No. 561,381.

To all whom it may concern:

Be it known that I, WALTER VAN BRAAM ROBERTS, a citizen of the United States, and a resident of Princeton, in the county of Mercer and State of New Jersey, have invented a new and Improved Loud-Speaking Tele hone Receiver, of which the followingis a all, clear, and exact description.

This invention relates to loud speaking receivers, and has particular reference to one in which the vibration of a plurality of diaphragms is more efliciently adapted for use in connection with loud speaking telephone receivers.

An object of the invention is to increase the magnification of amplitude of a loudspeaking device and eliminate any necessity for the use of fixed pivots, which are one of the causes of unnecessary friction.

Another object resides in the provision of means whereby the volume of sound is increased from a given available amount of power by reason of the elimination of friction in the various parts.

A further object resides in the particular construction and arrangement of parts which are hereinafter described and claimed and shown in the accompanying drawings.

The invention is illustrated in the drawings, of whichigure 1 is an elevation of certain parts in section of one form of the device.

Figure 2 is a side elevation of the magnets and the armature.

The form of the invention shown in the drawings is a preferred form, although it is understood that modifications in the construction and arrangement of the parts and in the character of the materials used may be adapted without departing from the spirit of the invention.

In the commonest type of tele hone receiver a vibratory diaphragm is riven directly by an electromagnet. It is well known as above mentioned, through the similar,100

that the efiiciency of transformation of electrical ener to sound ener may be improved if t e electromagnet is employed to drive an armature which forms part of one end of a lever of pro er design, working on a ivot, and attac ed at the other end to a vi ratory diaphragm, which in this case need not be of magnetic material. Thus a small amplitude of motion of the armature may be and has been translated into a larger amplitude of motion of the diaphragm, resulting in an increased acoustic output.

One of the objections, however, to this method of connecting up the motion of the armature is the mechanical friction at the fixed pivot of the lever. My invention aims to eliminate this friction by eliminating the necessity for the use of a fixed pivot. The main feature of the invention whereby I eliminate this friction resides in the fact that I use two diaphragms, one connected at each end of the lever system of which a vibrating armature forms a part. By this means an increased volume of sound is obtained with the same available amount of electrical ower. This is in addition to the increase in efficiency resulting from the elimination of the pivot.

This invention may, of course, be embodied in many forms, of which one of the preferred forms is shown in the drawings, and comprises two fixed horseshoe magnets in which the poles are represented as N, S and N, S. These magnets may be of the permanent type or they may be electrically energized by any special direct current (not shown). 1 is a fixed coil which is adapted preferably, to be energized by any suitable varying electrical current which is to be reproduced as sound. The coil 1 is designed to magnetize a movable soft iron armature 2. The armature2 is connected at each end by rods 3 and 4 to vibratory diaphragms 5 and 6. These diaphragms are connected in any desired manner to casings or tubes 7 and 8 which may, in any well known manner not shown, be connected to a horn or amplifying device. The connection between eac rod and its diaphragm is, however, owing to the slight inevitable flexibility of the rods and .of each diaphragm, not so rigid as to fail to permit the desired vibration of the system. The diaphragm and the rods may be of non-magnetic material. The sound output from the diaphragms is led,

tubes or casings 7 and 8 to any amplifying or megaphonic device.

The varying electrical current which it is desired to reproduce as sopnd is passed through the coil 1. Thus the intensity and direction of the polarity of the armature 2 are varied; and, as a result, the armature experiences a twist, since its two ends tend to move in opposite directions in the two constant ma netic fields. On account of the symmetry 0 the design, the resultant motions of the diaphragms 5 and 6 will be alike. The ratio of the am litude of their motion to theamplitude 0 motion of the armature may be made considerably greater thanunity by choosing the desired length for the rods 3 and 4.

It should be understood" that gravity plays no art in the operation of t is device. Alt ough in Figure 1 the diaphragms are shown as directing their sound outputs along the vertical direction, this is not essential, and the apparatus would operate equally well in any other position.

The sound outputs of the two diaphra s are equal in intensity and phase just be ore they are made to combine in a horn or magnifying device (not shown), since the casings or tubes 7 and 8 are exactly similar, and the arrangement of the diaphragms 5 and 6 is exactly symmetrical. Thus the total volume of sound obtained with this device corresponds to anamplitude of sound waves in air twice as'great as would be excited if the sound output of only one of the diaphragms were led to the said 'horn. Thus the efiiciency of this device, that is the ratio of the total power of the sound output to the electrical mately double by the utilization of the sound output from two diaphragms.

As regards the feature of this invention which consists in the abolition of the fixed pivot, it is not however, essential that the acoustic output from both diaphra ms be utilized. Thus the ear could be app ied directly over one of the diaphragms, and in this case it may be desirable t place in front of the other diaphragm a small enclosed chamber designed to imitate the acoustic impedance of the car, so as to preserve completely the symmetry of the stern. Of course, it is not essential that t is invention be used as a loud speaker; it may be arranged to be employed as an ordinary telephone receiver.

The essential feature of this invention is the employment of two diaphragms connected to a vibrating armature disposed in a power absorbed, is approxi- 1,4eo,ass

magnetic field whereby a fixed pivot is eliminated. The receiver contemplated in accordance with this invention offers two advantages over other receivers. First, on account of the absence of a fixed pivot the lossof energy caused by such a pivot is obviated. Even if a pivot is employed with the arrangement described herein, it will introduce but little loss of energy, since the armature and the lever system are supportedby the diaphragms. Secondly, the substitution of an additional diaphragm offers in itself the advantageous capability of increasing the amplitude and volume of the sound issuing from the receiver.

What I claim isz 1. In a telephone receiving device, a vibratory armature, a substantially fixed magnetic field disposed transversely across each end of the armature, a coil embracin the middle portion of said armature'and a apted to receive speech currents, the magnetic action of the currents in said coil changing the polarity of the ends of the armature, levers extending in opposite directions from the ends of said armature in a line substantially parallel to the axis of the armature, and dlaphragms connected to the ends of said levers, said armature being supported from said diaphragms.

2. Ina telephone receiving device, a vibratory armature, a substantially fixed ma netic field disposed transversely across eac end of the armature, a coil embracing the middle portion of said armature and adapted to receive speech currents, the magnetic action of the currents in said coil changing the polarity of the ends of the armature, levers extending in opposite directions from the ends of said armature in a line substantially parallel to the axis of the armature,

the ends of said levers bent respectively in opposite directions at right angles to the axis of the armature, and diaphragms connected to the ends of the levers.

WALTER VAN BRAAM ROBERTS. 

